One kind of hydraulically controlled variable deflection roll is disclosed by the 1964 Kusters et al U.S. Pat. No. 3,131,625.
This roll comprises a rotative shell forming an external work-rolling surface and a cylindrical inside. A fixed shaft extends through the shell's inside with radial clearance permitting independent transverse deflection of the roll and shaft. The shaft has a longitudinally extending series of radially extending cylinders formed by blind bores in the shaft. Each cylinder contains a single reciprocating piston for applying the roll deflection force between the shaft and the shell via a bearing shoe bearing on the shell's cylindrical inside.
When in use with the roll rotating against a counterroll to form a nip through which flat work can be rolled, hydraulic pressure is introduced uniformly to the cylinders so their pistons force the shoes against the shell's inside to control the shell's contour. The reaction is carried by the shaft which functions as a beam and consequently bends under the beam stress it receives, whether the roll's controlled contour is straight or curved.
Excepting for the cylindrical bores and relatively small hydraulic liquid feed passages to the various cylinders, the fixed shaft is made of solid metal. Its maximum diameter is limited by the need for clearance between it and the shell's inside. The radial extent or depth of the bores affect the beam strength and stiffness of the shaft, so it is desirable to have the bores as short or shallow as possible. It has been necessary to make the cylinders formed by the bores, and their pistons, of large diameter to provide adequate roll deflection force without using excessive hydraulic pressure.
It is common rule that to avoid a piston tilting or canting in its cylinder. The piston must have a guided length 1.5 times its diameter, necessarily requiring its cylinder to be substantially longer to accommodate the piston's working stroke. It follows that in the case of the described roll the bores forming the cylinders must extend undesirably far into the fixed shaft in its radial direction with a consequent undesirable reduction in the shaft's beam strength and stiffness.
One possibility for reducing the depth of the bores in the shaft might be to reduce the working stroke length of the pistons so their cylinders or shaft bores could be shortened, or to substitute for the cylinders and pistons shorter bores containing hydraulically actuated bellows arrangements.
However, with the fixed shaft functioning as a beam and bending under the beam stress, its central portion in particular substantially increases its spacing or clearance from the inside of the shell. To accommodate this, the pistons, at least those at or near the center of the fixed shaft, must have the long working stroke length, and bellows arrangements would be required to expand more than compatible with a bellows wall thickness withstanding the hydraulic pressures required. Such problems become more complex when the roll is working against a counterroll not provided with deflection control means and which itself bends so as to require the shell to correspondingly bend in a direction opposite from the shaft's bending direction.
It is possible to journal the shell either rotatively on the fixed shaft iself or independently of the shaft by bearings in a frame which mounts the shaft and the necessary counterroll. In the latter instance, the fixed shaft can be mounted by the frame so that at the shaft's ends it can be displaced upwardly or downwardly relative to the shell so as to thereby decrease the clearance between the shaft and the shell opposite to the counterroll on the working side of the shell where it externally forms the nip with the counterroll. However, reduction of the clearance between the shaft and the shell's inside effected in this way cannot compensate for the fact that the shaft bends under its beam strength. Any effort to reduce the clearance between the shaft and shell's inside at the central part of the controlled deflection roll can only result in the clearance at the ends of the roll being reduced to an unsafe value or possibly resulting in the shaft coming in contact with the roll's inside.